Alarm initiating circuit for radiac system



Jan. 10, 1956 c. w. MAGNUSON ALARM INITIATING CIRCUIT FOR RADIAC SYSTEM Filed May 14, 1952 R mm NS E vw A M u w 1 L m wmOPOuhuO NM Y B mohouhwo ATTORNEYS United States Patent O ALARM INITIATING CIRCUIT FOR RADIAC SYSTEM Carl W. Magnuson, Baltimore, Md., assignor, by mesne assignments, to the United States of America as repre sented by the Secretary of the Navy Application May 14, 1952, Serial No. 287,786

1 Claim. (Cl. 340-213) Various alarm systems have been devised in the past to give electrical or mechanical indications to indicate a predetermined condition. Some of these systems utilize detectors such as photoelectric cells to detect changes in infrared radiation or changes in visible light. Other systems utilize various heat responsive devices. Still other systems involve the use of electric apparatus whose electrical characteristics change upon the occurrence of a predetermined condition.

All these systems have suffered from the disadvantage of being relatively insensitive at certain times. Furthermore it has been diflicult to combine a number of detection units so that an alarm will be actuated from any one of the units in a mutually exclusive manner. The present invention seeks to overcome such disadvantages by providing a plurality of detection units consisting of detectors in combination with alarm initiating circuits which are balanced to be very sensitive to changes in surrounding conditions. A very simple circuit arrangement is provided wherein a number of detection units may be combined to actuate an alarm common to all of them.

More specifically, each detection unit includes an electron tube having a grid that is biased to a desired voltage level, and a second electron tube having a grid whose bias is determined by a detector. The two electron tubes both include cathode follower resistors. The high potential sides of these resistors are tied together by a connection through the solenoid coil of a relay. The relay includes a normally open switch which controls the application of current to an alarm. At such time as the detector is actuated to vary the grid bias of the tube associated with it, current conduction through that tube will be changed. This creates a changed potential difference across the solenoid and of sufficient magnitude and direction to actuate the relay. When the relay is actuated the alarm is set off. Means are provided so that a plurality of detection units may be tied together to actuate a common alarm. Each unit may be arranged to be responsive to an external condition of a magnitude difierent from that which each of the other units is responsive to. This is provided by the use of multiple potentiometers arranged to vary the grid bias of the proper electron tube.

Accordingly it is an object of the present invention to provide an improved alarm circuit adaptable for use with various types of detectors.

Another object of the invention is to provide an improved alarm system wherein a plurality of detector units may be associated together to operate a common alarm in a mutually exclusive manner.

It is a final object of the invention to provide a radiation responsive alarm system including a plurality of detectors in combination with balanced circuits which will actuate a common alarm.

Other objects and many of the attendant advantages Fatented Jan. 10, 1956 of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing of the same in which:

Fig. 1 is a circuit diagram of a preferred embodiment of the invention; and

Fig. 2 illustrates a specific detector arrangement adapted for use with the circuit of Fig. 1.

Referring now to the drawings, there is shown in Fig. 1 individual detection units A and B. Unit A and Unit B are identical and their coaction will be fully described below.

Unit A includes detector 31 which may be a photoelectric cell, a photo-sensitive device, a heat-responsive device or any one of a number of similar equipments. Detector 31 provides a voltage which is impressed upon the grid of electron tube 3. This voltage may be either positive or negative as desired. Tube 3 includes an anode connected to a source of positive potential and a cathode tied to ground through cathode resistor 4. Electron tube 7 is used in combination with tube 3. Tube 7 includes an anode tied to a source of positive potential. The grid of this tube is connected directly to potentiometer 8. Potentiometer 8 controls the application of bias voltage from source 9 to the grid of electron tube 7. Current flowing through tube 7 must pass through cathode resistor 11 which has a grounded end and an end connected to armature 16 will make contact with contactor 17. When current passes through coil 14 from point 12 to point 13 armature 16 will make contact with contactor 18. Switch blade 19 may be moved into contact with contactor 20 or with contactor 21 depending upon which direction current will flow through coil 14. If detection unit A is so arranged that armature 16 will be pulled into contact with contactor 17, switch blade 19 is manually set in contact with contactor 20. If unit A is so arranged that armature 16 will be moved into contact with contactor 18, blade 19 is manually set to make contact with contactor 21. This is done in order that a circuit will be completed through alarm 22 from battery 23.

Detection unit B is identical with detection unit A. It comprises a detector 32, electron tube 33 having a cathode resistor 34 and eelctron tube 37 having a cathode resistor 41. Across the points 42 and 43 there is connected relay 44 having coil 45. When current flows from point 43 to point 42, armature 46 will be pulled into contact with contactor 47; when current flows from point 42 to point 43 armature 46 will be moved into contact with contactor 48. Switch blade 51 may be manually moved into contact with either contactor 52 or 53 depending on the direction in which current will flow through coil 45. The operation of detection unit B is controlled by the connection of the grid of tube 37 to potentiometer 55.

In Fig. 2 there is shown a typical heat responsive detector which may be used at 31 or 32 of Fig. l. Thermistor 60 and resistor 61 are in series connection across battery 62. An output voltage may be taken at point 65 and fed through resistor 66 to the grid of tube 3 or 33. Thermistor 60 will change its resistance upon the application of heat thereto. It may be of the type that increases in resistance or it may be of the type that decreases in resistance. Assuming that it increases in resistance when heat is applied, the voltage drop across it will increase. The drop across fixed resistor 61 will correspondingly decrease since the sum of the voltage drops across thermistor 60 and resistor 61 must always equal the fixed voltage across battery 62. Point 65 will accordingly be raised in potential with respect to ground as heat is applied to thermistor 6G, and a more positive grid bias is applied to tube 3.

The two detection units A and B operate in a similar manner. For purposes of explanation one mode of operation of unit A is described. Switch blade 19 is first moved adjacent contactor 20. Tubes 3 and 7 are arranged to conduct current continuously when no signal is applied from detector unit 31. The bias on the grid of tube 7 is set at some level determined by the setting of potentiometer 8 to cause the tube 7 to conduct more current than tube 3. Consequently the potential of point 12 with respect to ground will be more than the potential of point 13- with respect to ground because the voltage drop across resistor 11 will be more than the voltage drop across resistor Current flows from point 12 to point 13 but armature 16 will not complete a circuit through contactor 1S, alarm 22, and battery 23 because switch blade 19 is not in Contact with contactor 21.

Assuming that detector 31 produces a positive signal in response to a predetermined condition, an additional positive voltage will be placed on the grid of tube 3. When this voltage is great enough the grid of tube 3 will. be driven in a positive direction sufiiciently to increase conduction of current through the tube enough to raise the potential of point 13 with respect to ground above that of point 32 with respect to ground. This will cause a reversal of polarity of the voltage across operating coil 14 of relay 15. Armature 16 will be attracted to contactor l7 and a circuit through alarm 22 and battery 23 will be completed. It is seen that this type of operation causes actuation of the alarm 22 only after the detector 31 is actuated at greater than a predetermined threshold level which is determined by the setting of potentiometer 3.

It would also be possible to operate detection unit A so that tubes 3 and 7 are normally conducting and the potential of points 12 and 13 with respect to ground are identical. Consequently the application of the positive signal voltage from detector 31 would cause an increase in current flow through tube 3 with the result that the potential of point 13 would increase with respect to ground. This change in potential would act to cause a current flow through relay 15 id to move armature 16 adjacent con tactor 27. This will also complete a circuit through alarm 22. This arrangement would provide a very sensitive detcction system.

If detector 31 produces a signal of decreased potential upon actuation, the unit A may be operated so that tube 3 is normally conducting more current than tube 7. This would be brought about by suitable adjustment of potentiometer I) with respect to the non-actuated output voltage of detector 3i. Switch blade 59 would be moved into contact with contactor 2i. Assuming that detector 31. were of the type that produces a decreased output voltage when it is energized, as for example if thermistor 60 of Fig. 2 dropped in resistance value upon the application of heat, a more negative bias would be applied at the grid of tube 3 when the detector 31 became energized. Current flow through tube 3 would then be diminished and the potential of point 13 would drop below that of point 1.2. This reversal in polarity across coil 14 would cause current to flow from point 12 to point 13 and act to bring armature 16 into contact with contactor 18. Since switch blade 19 is in Contact with contactor 21, a complete circuit would be completed through alarm 22 and battery 23.

It is immaterial to the invention whether or not the signal voltage from detector unit 31 is positive or negative; it is immaterial whether or not the relay 15 is arranged to be actuated by an increased potential at point 12 or at point 13. The important feature involved is that the signal voltage developed by detector 31 will be effective to cause a reversal in polarity across relay 15 and thereby actuate alarm 22.

The unit B is shown to be tied in with detection unit A since there is a common connection to alarm 22. A plurality of units may be tied in with unit A in exactly the same manner. However, each unit is made to be more or less responsive than the others to an external condition by means of individual biasing means such as potentiometer 55 in the grid circuit of tube 37. By means of such a potentiometer, the grid at tube 37 may be set at exactly the same potential of the grid of tube 7, or it may be set at some different potential with respect to ground. if this latter arrangement is used, a different potential difference will be required to actuate the relay in the associated unit. Various modifications, such as detectors of varying sensitivity, different tube biasing means, etc., may be utilized and still remain within the scope of the present invention.

It should be understood that the foregoing disclosure relates to only a preferred embodiment of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and scope of the invention as set forth in the appended claim.

What is claimed is:

An alarm initiating circuit responsive to signals indicative of conditions a predetermined amount above or below ambient generated by a detecting device comprising, a detector, first and second electron tubes each having an anode, a cathode and a control grid, a common source of voltage supply for the anodes, a conductor directly connecting said detector with the control grid of said first tube, individualized equal resistors connecting the re spective cathode to ground, a variable bias source including a potentiometer having its movable tap connected directly to the control grid of said second tube for causing one or the other of said tubes to conduct more heavily than the other, a relay coil connected between said cathodes, a single two terminal armature associated with said coil initially adapted to contact one or the other of said two terminals as determined by the bias voltage applied to said second grid and operable in response to signals of a predetermined amount to reverse its contacts, a single pole double throw switch, conductors connecting said two terminals with the two contact positions of said switch respectively, an alarm circuit including a power supply therefor serially connected with said armature and said switch pole, said alarm circuit being energized in response to detected signals indicative of conditions a predetermined amount above ambient: when said switch pole is in one position and to conditions a predetermined amount below ambient conditions when said pole is in the other position depending on the initial position of said armature.

References Cited in the tile of this patent UNITED STATES PATENTS 

